Evaporator with oil return means



Nbv. 26, 1963 H. R. WILLIAMS 3,111,819

EVAPORATOR WITH OIL RETURN MEANS Filed Nov. 3, 1961 2 Sheets-Sheet 1 fave/pier .Harry 1?. VL ZZZmms' Nov. 2 1963 Filed NOV. 5, 1961 2 Sheets-Sheet 2 United States Patent 3,111,819 EVAPORATQR WITH UilL RETURN MEANS Harry R. Williams, Mnncleleirr, REL, assignor to Bell & Gossett Company, a corporation of Illinois Filed Nov. 3, 19st, Ser. No. 150,052 6 Claims. (til. tin-471) This invention relates to an expansion evaporator for use in a refrigeration system and more particularly is concerned with providing an improved evaporator head structure.

In a flooded type evaporator, a definite level of liquid refrigerant is maintained. Gas velocities through such an evaporator usually are too low to entrain and return oil to the compressor. Consequently, it has been necessary to employ rather elaborate means to return the oil that becomes entrapped. The oil, being miscible with the refrigerant tends to accumulate in high concentration in the evaporator and this can only result in less efficient heat transfer.

In a direct expansion evaporator, no definite level of liquid refrigerant is maintained. Liquid refrigerant is boiled off as fast as it enters and gas velocities are high enough to entrain oil and return it to the compressor. In the prior art, direct expansion evaporators have at times been guilty of suddenly dumping liquid into the compressor and this dumping or slugging can frequently cause broken valves, pistons or connecting rods. To avoid this, the expansion valve has been set to a pressure to insure boiling off of the refrigerant at a point well short of the full length of the evaporator coils. Thus, part of the heat transfer area of the evaporator is used to superheat the refrigerant vapor and this does not make full utilization of the evaporators heat transfer area.

The principal object of the present invention is to provide an evaporator offering full utilization of the available heat transfer area with reliable surge protection and effective oil return to the compressor.

Another object of the invention is to provide an evaporator having an expansion chamber equipped with a heat exchange coil that is in series in the refrigerant supply line.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the accompanying drawings forming a part of this specification and in which like numerals are employed to designate like parts throughout the same:

FIG. 1 is a diagrammatic illustration of a refrigeration circuit having an evaporator arrangement in accordance with this invention;

FIG. 2 is an enlarged sectional view through the head of the evaporator; and

FIG. 3 is a diagrammatic illustration of the refirigera tion circuit employing an alternative form of evaporator arrangement.

Referring now to the drawings, a typical refrigeration system embodying the principles of this invention, is illustrated in FIG. 1 as consisting of a refrigerant compressor 10, a condenser 11, an expansion valve 12, and an evaporator 13, all connected in a series circuit relationship. Freon flows through the circuit in the directions indicated by the arrows applied to FIG. 1 and the supply line 14 through which liquid Freon flows from the condenser to the expansion valve includes a heat exchange coil 14C connected in series therein and physically located within the evaporator 1.3.

The evaporator arrangement of this invention promotes full utilization of the heat transfer area While providing for metering liquid back to the compressor at a controlled rate to avoid undesirable accumulations of oil in the evaporator and to provide surge protection for the com- 3,111,819 Patented Nov. 26, 1963 pressor. For this purpose, the evaporator 13 illustrated herein for purposes of disclosure comprises a chiller body 15 equipped with the usual evaporator coils 16 and an evaporator head 17. The evaporator coils 16, as illustrated herein, are of half loop configuration and have their intake and discharge ends mounted in suitable openings provided in a common divider plate 18 that is fixed in sealed relation between the body and head structures.

The evaporator head has an internal wall 19 partitioning the head into an infeed chamber 20 for supplying refrigerant from the expansion valve 12 to the intake ends of the evaporator coils 16 and an expansion chamber 21 for receiving and storing liquid and vapor exiting from the discharge ends of the evaporator coils.

A suction line 22 between the evaporator and the compressor originates with a dip tube 23 projecting part way into the expansion chamber. A metering tube 24 is also shown in the expansion chamber and has its lower end spaced slightly above the bottom of the expansion chamber and has its upper end projecting Well into the dip tube fitting and directed in line with the high velocity gaseous refrigerant moving through the suction line to produce an aspirating effect to draw out any liquid accumulating Within the bottom of the expansion chamber 21. The heat exchange coil 14C that is in series in the supply line to the expansion valve 12 is shown encircling the dip tube 23 Within the expansion chamber 21 and since the liquid in the supply line to the expansion valve is usually at a higher temperature than the gaseous refrigerant in the expansion chamber, heat will transfer from the coil to the refrigerant in the expansion chamber.

In the operation of the refrigeration system equipped with an evaporator arrangement in accordance with the present invention, the expansion valve 12 for regulating the flow of liquid from the supply line into the evaporator coils is set at a pressure value such that some refrigerant will remain in liquid form throughout substantially the entire length of the coils and will not boil off to gas until the refrigerant reaches the discharge ends of the coils. In effect, therefore, refrigerant is returned through the suction line at 0 superheat. Some carry-over of liquid refrigerant from the discharge end of the evaporator coils can be tolerated without danger of slugging because of the storage capacity afforded by the expansion chamber 21. In general, the liquid reaching the expansion chamber will boil off to gas immediately but, if required, some can be stored in the reservoir at the bottom of the expansion chamber. Any liquid collecting in this reservoir is metered back to the compressor in amounts the compressor can safely handle. The presence of the supply line heat exchange coil 14C accelerates the boiling off of any liquid tending to collect in the expansion chamber and serves to superheat refrigerant vapor thereby eliminating the need for a suction line heat exchanger. In lie-u of connecting the heat exchange coil 14C in series in the refrigerant supply line, the coil may be connected to a steam or hot Water line for supplying heat to refrigerant in the expansion chamber.

An important advantage of this arrangement is that the available heat transfer area presented by the evaporator coil is fully utilized and this increases the efficiency of the system without sacrificing surge protection for the compressor. In addition, the metering tube 24 provides an efiicient and simple means for returning oil and liquid refrigerant to the compressor at a controlled rate. The oil entrainment action of the metering tube is reliable because of the relatively high gas velocities of the refrigerant moving from the expansion chamber 21 through the suction line 22 to the compressor.

A gravity drain tube T is shown exiting from the bottom of the evaporator head to permit draining the system 3 of FIG. 1 should that be desired. A plug P normally seals the gravity tube T,

In FIG. 3 an alternative evaporator arrangement is shown in a refrigeration circuit which is identical with that of FIG. 1 and is correspondingly numbered with the exception that the drain tube T shown exciting from the bottom of the evaporator head is of capillary size and leads through a capillary tube extension 349 to a point of the suction line 33 that is at a lower elevation. Thus the capillary line 30 provides a gravity flow for metering liquid at a controlled rate from the reservoir in the bottom of the head to the suction line. With this arrangement, the Venturi tube 24 employed in the head of PEG. 2 may be omitted.

The operation of the circuit of FIG. 3 is essentially similar, the principal purpose of the capillary line 38 is to return oil. However, on occasions when liquid collects in the evaporator head, some of this liquid will be returned through the capillary line while the remainder is being boiled off to the expansion chamber and passed directly to the suction line. The capillary line is selected at a size having sufiicient restriction to flow so that liquid is metered back only in amounts that the compressor can handle.

It should be understood that the description of the preferred form of the invention is for the purpose of complying with Section 112, Title 35, of the US. Code and that the appended claims should be construed as broadly as the prior art will permit.

What is claimed is:

1. In a refrigeration circuit, in combination, a direct expansion evaporator having a chiller body, a hollow head on one end of said body and providing an expansion chamber, an infeed line to said evaporator, evaporator coils disposed in said body and connected at one end to communicate with said infeed line and connected at the other end to discharge directly into said head at an elevated point therein, means including an adjustable expansion valve, series connected in said infeed line, regulating the pressure condition of liquid refrigerant. entering said evaporator coils to enable refrigerant to remain in liquid form throughout substantially the entire length of the coils and to boil off to low pressure gaseous refrigerant substantially directly as the refrigerant discharges into said expansion chamber, a suction line leading from an elevated point in the expansion chamber for returning low pressure gaseous refrigerant to a compressor for the circuit, and means leading from the bottom of said chamber to said suction line for metering liquid from the chamber to the suction line at a controlled rate.

2. In a refrigeration circuit, in combination a direct expansion evaporator having a chiller body, a hollow head on one end of said body and providing an expansion chamber, an infeed line to said evaporator, evaporator coils disposed in said body and connected at one end to communicate with said infeed line and connected at the other end to discharge directly into said head at an elevated point therein, means including an adjustable expansion valve, series connected in said infeed line, regulating the pressure condition of liquid refrigerant entering said evaporator coils to enable refrigerant to remain in liquid form throughout substantially the entire length of the coils and to boil off to low pressure gaseous refrigerant substantially directly as the refrigerant discharges into said expansion chamber, a suction line leading from an elevated point in the expansion chamber for returning low pressure gaseous refrigerant to a compressor for the circuit and a metering tube in said expansion chamber and having an intake end at the bottom of said expansion chamber and a discharge end projecting into the suction line for producing an aspirating action in response to flow of low pressure gaseous refrigerant through the suction line to meter liquid into dthe suction line at a controlled rate thereby providing surge protection for the compressor.

3. In a refrigeration circuit, in combination a direct expansion evaporator having a chiller body, a hollow head on one end of said body and providing an expansion chamber, an infeed line to said evaporator, evaporator coils disposed in said body and connected at one end to communicate with said infeed line and connected at the other end to discharge directly into said head at an elevated point therein to directly boil off liquid refrigerant emerging therefrom, a suction line leading from an elevated point in the expansion chamber for returning low pressure gaseous refrigerant to a compressor for the circuit and a gravity fiow metering tube external of said expansion chamber and having an intake end leading from the bottom of the expansion chamber to a point at lower elevation in the suction line to meter liquid into the suction line at a controlled rate thereby providing surge protection for the compressor.

4. In a refrigeration circuit, in combination a direct expansion evaporator having a chiller body, a hollow head on one end of said body and providing an expansion chamber, an infeed line to said evaporator, evaporator coils disposed in said body and connected at one end to communicate with said infeed line and connected at the other end to discharge directly into said head at an elevated point therein to directly boil off liquid refrigerant emerging therefrom, a suction line leading from an elevated point in the expansion chamber for returning low pressure gaseous refrigerant to a compressor for the circuit, a heat exchange coil connected in series in said infeed line and disposed within said expansion chamber in heat exchange relation to refrigerant therein, and means leading from the bottom of said chamber to said suction line for metering liquid from the chamber to the suction line at a controlled rate.

5. In a refrigeration circuit, in combination a direct expansion evaporator having a chiller body, a hollow head mounted directly on said body, said head having internal Wall structure partitioning the same into a refrigerant intake chamber and a refrigerant expansion chamber of substantially greater volume than the intake chamber, an infeed line leading into said intake chamber, evaporator coils disposed generally horizontally in said body and connected at one end into said intake chamber and connected at the other end to discharge directly into said head at an elevated point therein, means including an adjustable expansion valve, series connected in said infeed line, regulating the pressure condition of liquid refrigerant entering said evaporator coils to enable refrigerant to remain in liquid form throughout substantially the entire length of the coils and to boil off to low pressure gaseous refrigerant substantially directly as the refrigerant discharges into said expansion chamber, a suction line leading from an elevated point in the expansion chamber for returning low pressure gaseous refrigerant to a compressor for the circuit, and means leading from the bottom of said expansion chamber, to said suction line for metering liquid from the chamber to the suction line at a controlled rate.

6. In a refrigeration circuit, in combination a direct expansion evaporator having a chiller body, a hollow head mounted directly on said body, said head having internal wall structure partitioning the same into a refrigerant intake chamber and a refrigerant expansion chamber of substantial! greater volume than the intake chamber, an infeed line leading into said intake chamber, evaporator coils disposed generally horizontally in said body and connected at one end into said intake chamber and connected at the other end to discharge directly into said head at an elevated point therein to directly boil off liquid refrigerant emerging therefrom, a suction line leading from an elevated point in the expansion chamber for returning low pressure gaseous refrigerant to a compressor for the circuit, a heat exchange coil conline at a controlled rate thereby providing surge protecnected in series in said infeed line and disposed within tion for the compressor. said expansion chamber in heat exchange relation to refrigerant therein, and a metering tube in said expansion References Cited in the file of this P chamber and having an intake end at the bottom of said 5 UNITED STATES PATENTS expansion chamber and a discharge end projecting into 1,854,997 pl Apr. 19, 1932 the suction line for producing an aspirating action in 1 73 519 li Aug 23 193 response to flow of low pressure gaseous refrigerant 1384,187 P lti ()q; 25, 1932 through the suction line to meter liquid into the suction 3,012,414 La Porte Dec. 12, 1961 

1. IN A REFRIGERATION CIRCUIT, IN COMBINATION, A DIRECT EXPANSION EVAPORATOR HAVING A CHILLER BODY, A HOLLOW HEAD ON ONE END OF SAID BODY AND PROVIDING AN EXPANSION CHAMBER, AN INFEED LINE TO SAID EVAPORATOR, EVAPORATOR COILS DISPOSED IN SAID BODY AND CONNECTED AT ONE END TO COMMUNICATE WITH SAID INFEED LINE AND CONNECTED AT THE OTHER END TO DISCHARGE DIRECTLY INTO SAID HEAD AT AN ELEVATED POINT THEREIN, MEANS INCLUDING AN ADJUSTABLE EXPANSION VALVE, SERIES CONNECTED IN SAID INFEED LINE, REGULATING THE PRESSURE CONDITION OF LIQUID REFRIGERANT ENTERING SAID EVAPORATOR COILS TO ENABLE REFRIGERANT TO REMAIN IN LIQUID FORM THROUGHOUT SUBSTANTIALLY THE ENTIRE LENGTH OF THE COILS AND TO BOIL OFF TO LOW PRESSURE GASEOUS REFRIGERANT SUBSTANTIALLY DIRECTLY AS THE REFRIGERANT DISCHARGES INTO SAID EXPANSION CHAMBER, A SUCTION LINE LEADING FROM AN ELEVATED POINT IN THE EXPANSION CHAMBER FOR RETURNING LOW PRESSURE GASEOUS REFRIGERANT TO A COMPRESSOR FOR THE CIRCUIT, AND MEANS LEADING FROM THE BOTTOM OF SAID CHAMBER TO SAID SUCTION LINE FOR METERING LIQUID FROM THE CHAMBER TO THE SUCTION LINE AT A CONTROLLED RATE. 